Prosecutions boss Mokotedi Mpshe withdrew the charges following representations from Zuma which included the so-called spy tapes.

The tapes were secret recordings of Scorpions head Leonard McCarthy discussing the timing of charging Zuma, in a bid to influence the outcome of the African National Congress (ANC)'s Polokwane Conference in December 2007.

Advocate Sean Rosenberg says it was inexplicable that after weighing up the evidence against Zuma, that Mpshe's decided to withdraw the prosecution.

"Let's accept there was offence of conduct on the part of Mr McCarthy and it was unrelated with the decision to prosecute, to the extent that it had any influence and it was related to the timing."

Rosenberg says the decision was irrational and impulsive.

"The approach he took to merely conclude that the abuse in question was a sufficient affront to his sense of propriety and that without more prosecution fell to be discontinued. The nature of the conduct, being the political interference in the timing of the service of the indictment, was limited and insignificant essentially."

Advocate Hilton Epstein says McCarthy's conduct was highly irregular.

"He is manipulating when the charges were brought and doing it to ensure that president Mbeki gets elected at Polokwane."

The National Prosecuting Authority (NPA) has argued that McCarthy's conduct should be minimized because he manipulated the prosecutorial process to influence the ANC's conference

Rosenberg says when weighing the evidence against the president, the decision to withdraw the prosecution was irrational.